The samples of Hypoeutectic and hypoeutectic chromium white cast iron were prepared by pressure casting. The effect of solidification pressure on microstructure, phase composition and mechanical properties of chromium white cast iron was studied. The composition and formation mechanism of microstructure of chromium white cast iron under high pressure were revealed. The competitive growth of eutectic phase and the nucleation and growth mode of carbide were discussed
(1) With the increase of solidification pressure, the eutectic structure of Hypoeutectic and hypoeutectic chromium white cast iron is obviously refined. Hypoeutectic chromium white cast iron (alloy 1 #) changes from large white lath structure to small white structure, showing short rod and equiaxed structure; The eutectic structure of near eutectic chromium white cast iron (alloy 2) transforms from lath to curved surface strip, short rod and polygon; When the pressure increases to about 160 MPa, the eutectic spacing is only half of that of normal pressure solidification.
(2) With the increase of solidification pressure, the growth mode of eutectic phase in Cr white cast iron changes from parallel growth to alternate competitive growth. The results show that there is a quantitative relationship between the pressure P, t and RS. with the increase of pressure, the overall undercooling △ t of eutectic solidification increases and the radius rs of eutectic dendrite tip decreases.
(3) The effect of pressure on Solidification Microstructure of Cr white cast iron decreases with the increase of solidification rate. The effect of pressure on the microstructure morphology (eutectic spacing, eutectic volume and primary phase size) of the samples near the die and the position of the indenter, i.e. the place with higher solidification rate, is relatively small.
(4) With the increase of solidification pressure, the nucleation rate and total content of carbides in hypoeutectic alloy 1 and near eutectic alloy 2 are greatly increased. The volume fraction of carbide in alloy 1 is about 2 times of that in normal pressure solidification; In alloy 2, the content of carbide increases about 1.5 times.
(5) With the increase of solidification pressure, the growth mode of eutectic carbide in solidification structure of chromium white cast iron changes from facet growth to non facet growth; With the increase of solidification pressure, the inclusion growth of primary carbides in the solidification structure of alloy 2 is accelerated.
(6) With the increase of solidification pressure, the amount of m3c type carbides in low chromium white cast iron decreases and M7C3 type carbides increase; The content of M23C6 carbide in high chromium white cast iron decreases and M7C3 carbide increases.
(7) When the solidification pressure is increased to 170 MPa, the impact wear resistance of alloy 1 is about 1.5 times of that at normal pressure, and that of alloy 2 is also increased by about 25% at 160 MPa; The hardness of alloy 1 increases about 17% at 170 MPa, and that of alloy 2 increases about 25% at 160 MPa; The impact toughness of alloy 1 # is not improved with the increase of pressure, but the impact toughness of alloy 2 # is about 1.5 times higher than that at normal pressure. The fine grain strengthening under pressure, the transformation of carbide morphology, the increase of carbide content and the decrease of defects in microstructure are all important factors to improve the impact wear properties of the alloy.